Watts, Newton-Meters, Power & Torque - Making Sense of E-bike Motors
If you’re considering shopping for an electric bike, power and torque are the two most common numbers to describe its performance. Electric bike power is typically measured in watts (W), whereas torque uses the Newton-meter (Nm) unit.
Power and torque affect the performance of all electric bike systems, whether you’re shopping for affordable electric bikes for commuting or high-performance Trek electric bikes. Understanding what these units mean and how they affect your e-bike’s capabilities will help you choose a model that best suits your needs.
How E-Bike Motors Work
The role of an electric bike motor is to provide electrically powered assistance. Unlike a moped, scooter or motorcycle, which feature independent throttles, an e-bike motor only delivers power when you pedal.
The motor is powered using electric energy drawn from the battery, similar to a combustion engine powered by burning a fuel and air mixture. Depending on the motor’s specifications, it may generate varying amounts of maximum torque and power.
The torque and power numbers determine the electric motor’s performance and overall capabilities, including maximum speed and pedal assist level on the road and when riding up inclines.
What is Torque?
Torque is a measurement of rotational force. In engines, it measures how hard the engine is turning. The more torque an e-bike motor has, the more force it can apply to the drivetrain. In broad terms, a higher torque propels the bike forward harder.
All types of electric bikes benefit from better torque. A higher torque rating broadly translates into better acceleration, particularly from a standstill, making it an excellent feature for road electric bikes. Trek and trail e-bikes with more torque also have better hill-climbing performance.
What is Power?
Power is a measurement of energy. An engine power rating indicates the maximum amount of energy it can output. Engine power is calculated by multiplying the engine’s torque by the crankshaft’s angular speed.
For example, in motor vehicles, crankshaft speed corresponds to engine RPM, indicated by a tachometer. On electric bikes, the crankshaft’s speed depends on how fast the rider pedals and which gear the shifter is set to.
The more power an electric bike has, the more efficient the motor’s electric assistance and the less effort the rider needs to pedal. This benefit is especially noticeable when riding up hills and inclines. More power lets the e-bike handle higher loads without struggling, such as additional cargo or a passenger.